Methods for producing aldehydes by the hydroformylation of an olefinically unsaturated organic compound with carbon monoxide and hydrogen in the presence of a rhodium-phosphorus complex catalyst and free phosphorus ligand are well known in the art as seen e.g. by the basic low pressure oxo hydroformylation process of U.S. Pat. No. 3,527,809 and the rhodium catalyzed liquid recycle hydroformylation process of U.S. Pat. No. 4,148,830.
For instance, U.S. Pat. No. 3,527,809 discloses a basic hydroformylation process wherein olefinically unsaturated organic compounds are hydroformylated with carbon monoxide and hydrogen in the presence of a rhodium-phosphorus complex catalyst and free phosphorus ligand to produce aldehydes in high yields at low temperatures and low pressures.
It is also known that under such hydroformylation conditions, some of the product aldehydes condense to form higher boiling aldehyde condensation by-products, such as dimers, trimers and the tetramers. U.S. Pat. No. 4,148,830 discloses the use of these higher boiling liquid aldehyde condensation by-products as a reaction solvent for the catalyst which also makes an excellent carrier for a continuous liquid recycle process. For example, such continuous liquid recycle processes, involve removal from the reactor of some of the liquid reaction aldehyde product solution containing aldehyde product, the solubilized rhodium-phosphorus complex catalyst, free phosphorus ligand and the higher boiling aldehyde condensation by-products, and separating the aldehyde product therefrom by rapidly volatilizing the aldehyde product. The volatilized aldehyde product and non-volatilized catalyst containing liquid reaction solution is then disengaged in a gas-liquid separator, wherein the vaporized aldehyde product vapor stream is passed overhead for recovery and the remaining condensed non-volatilized catalyst containing liquid reaction solution removed from the bottom and recycled back to the reactor.
However, a disadvantage found attendant with liquid catalyst recycle hydroformylation processes is the loss of phosphorus ligand during the process due to containment of volatilized phosphorus ligand in the vaporized aldehyde product stream obtained upon the volatilized separation of the aldehyde product from the liquid catalyst containing reaction product solution. In commercial scale operations such ligand loss can not only represents a stiff economic penalty due to the physical loss of the ligand, but renders further processing of the crude aldehyde product necessary if damage to downstream aldehyde hydrogenation system catalysts employed in producing alcohols from the aldehyde is to be prevented or at least minimized. For instance, a primary known use of such aldehydes is to produce alcohols via hydrogenation and phosphorus ligand contained in the crude aldehyde product has been found to cause deactivation of such hydrogenation catalysts.
Attempts to purify the crude aldehyde product by passing the volatilized aldehyde product through sophisticated entrainment equipment such as packed columns or trays is not considered a satisfactory answer to the problem. While such sophisticated methods may be suitable for removing and recovering entrained liquids in the vaporized aldehyde product steam they may also promote the formation of more higher boiling aldehyde condensation by-products. Likewise purification of the crude aldehyde product by condensation and redistillation only serves to also further promote aldehyde product loss by the formation of more higher boiling aldehyde condensation by-products, which disadvantage is further compounded by the direct loss of even more aldehyde that remains with the condensation by-products during such a separation procedure.
Thus there remains a need in liquid catalyst recycle hydroformylation for a simple and effective method for selectively removing and recovering the vaporized phosphorus ligand contained in the vaporized aldehyde product stream obtained during a continuous liquid recycle rhodium catalyzed hydroformylation process.